This Application is a 371 of International Application No. PCT/NL00/00007, filed Jan. 5, 2000.
1. Field of Invention
The invention relates to a vacuum control system for controlling vacuum while milking an animal.
2. Background of the Invention
In known vacuum control systems the vacuum pump runs at a constant rotational speed of approximately 1,500 revolutions per minute and the regulator comprises a mechanical valve with the aid of which air is admitted to the vacuum control system, so that a desired vacuum level is maintained in the system. If the regulator operates properly, the vacuum level is independent of the air consumption of the teat cup or a pulsator, if any. In that case the vacuum pump displaces a quantity of air of approximately 400 liters per minute. As a result, the vacuum is maintained within the maximally allowed deviation from the desired value, even in the situation of an open teat cup. If all the teat cups are connected to the teats of an animal to be milked, this means that the greater part of the 400 liters of air per minute flows through the mechanical valve of the regulator. This has the disadvantage that the energy consumption of the vacuum pump is high, because the pump is always displacing the maximum quantity of air. The vacuum level further depends on the pump capacity. Another disadvantage is that, if it is desired to guarantee the stability of the vacuum, level in the long term, it is necessary to check the mechanical valve regularly, such valve not having a calibration point.
An object of the invention is to obviate the above-mentioned drawbacks or at least to minimize them.
In accordance with the invention, the above object of the invention is to achieved by means of using a speed regulator, preferably a frequency regulator to control vacuum pump rpm or using an electronic valve to control the amount of air admitted to the system or by using both controls. In this manner it is possible to reduce the number of revolutions of the vacuum pump during milking when the air consumption is very low, as a result of which much energy is saved relative to known systems. Because of the fact that it is possible to select a higher rotational speed of the pump than the situation of the existing pump, that is, for example, 3,600 revolutions per minute, it is further possible to displace the same quantity of air of 400 liters per minute with a smaller pump. A further advantage of the frequency regulator is that the stability of the vacuum level can be guaranteed in the long term. The frequency regulator also offers the possibility of controlling the vacuum level per animal or per teat.
A further advantage is that by means of the electronic valve, which is known per se from automotive engineering, it is possible to anticipate vacuum fluctuation because of the fact that the valve comprises a very fast-acting control valve. In this manner a very stable vacuum level can be guaranteed in the situation of suddenly occurring alterations in the system, such as, for example, may occur when a teat cup is disconnected from a teat.
According to an inventive feature, a vacuum sensor is connected to the regulator. By means of the vacuum sensor, it is possible to activate the frequency regulator on the basis of the measured vacuum.